An integrated circuit may include redundant components that can be used to substitute damaged componentry. For example, one type of memory circuit includes a dynamic random access memory (DRAM) array of memory cells. The memory cells are arranged in rows and columns, each of which is addressable for purposes of storing a bit of information. As the density of memory cells increase, the number of faulty cells also increases during the fabrication process. To reduce the effect of faulty cells, redundant memory cells, or rather redundant sections of memory cells may be used to repair a damaged section of the array, wherein the damaged section includes one or more damaged memory cells.
A testing process is implemented to determine whether a section of the memory is damaged. In that manner, it can be determined which rows and columns of memory cells, and more particularly, which sections of the memory array, need to be repaired. The testing process may be implemented externally from the device containing the memory array, or internally using failure diagnosis circuitry built into the device (e.g., integrated circuit including the memory device).
Once a damaged section of the integrated circuit is identified, the repair process includes replacing the damaged section with a redundant resource. For instance, in the memory array, selection of the redundant section may be achieved through the application of fuse circuitry. More specifically, a fuse that is associated with a redundant section may be blown, such that when the fuse is intact, the original but later damaged section of memory is accessed for memory storage, but when the fuse is blown, the redundant section is then used for memory storage instead of the damaged section. Various techniques may be used to program the memory array for repair, and more particularly to blow the fuse for selection of the redundant section. All of these techniques have associated failure rates, in which the selected fuse is only partially blown and not fully blown.
In the case of a partially blown fuse, the integrity of the memory array is at risk. A partially blown fuse may in some cases still allow the use of the damaged section of the memory array, instead of the desired redundant section. In other cases, the partially blown fuse works properly, but only temporarily, as the redundant section is selectable over the damaged section. However, over time, the partially blown fuse will return to its original state and act as an intact fuse, at least with regards to the memory controller used for selecting between the damaged and redundant sections of the memory array. For instance, the partially blown fuse may undergo passive oxidation, which will tend to return the fuse to its original state (e.g., intact and unblown).
During the repair process, a test may be performed to check whether the fuse has been blown. However, these tests are not designed to detect partially blown fuses. As such, a partially blown fuse under traditional testing will appear to be fully blown, when in fact the opposite is true. In that case, because the partially blown fuse still looks like an intact fuse to the memory controller, the damaged section of the memory is improperly used for memory access and control, instead of the intended selection of the redundant section. This will introduce storage errors as information continues to be stored in the damaged section of the memory array.